Project Summary Ultrafine particles (UFPs) in the ambient air have been, and continue to be, an important environmental health concern. Thermal processes such as diesel engine and power plant combustions as well as photochemical processes can generate high concentration UFPs in the ambient environment. UFPs inevitably could be inhaled by the general public living in urban communities. The inhalation and the consequent deposition of UFPs in the human lower airways could lead to adverse health effects such as pulmonary impairment, cardiovascular disease, and even lung cancer. Therefore, from the viewpoint of environmental health, it is significant to investigate the deposition of inhaled UFPs in the human respiratory tract in order to correctly estimate the associated UFP inhalation dosimetry for environmental health pertinent etiology, exposure assessment, and risk analysis research. However, due to the restrictions of the current experimental approach as well as the complicated morphology of the ambient UFPs such as the diesel exhaust particles, no studies have been carried out to investigate the deposition of inhaled ambient UFPs in the human respiratory tract. As a result, ambient UFP respiratory deposition data is deficient and the related inhalation dosimetry remains unknown. With this in mind, to overall advance the experimental approach of ambient UFP respiratory deposition studies for correctly estimating the inhalation dosimetry, the objective of the proposed research is to develop a full-function Mobile Aerosol Lung Deposition Apparatus (fMALDA) and apply fMALDA for correctly estimating the UFP respiratory deposition and associated inhalation dosimetry in urban communities with various toxic chemical constituents. To achieve this objective, two specific aims are proposed. The Specific Aim 1 is to design, fabricate, and test the fMALDA in the laboratory, and the Specific Aim 2 is to quantify the respiratory deposition rates of chemicals on UFPs in human airways using fMALDA in urban communities. The long-term goal of this research is to apply fMALDA to various urban communities having UFP exposure concerns to estimate associated UFP inhalation dosimetry for specific chemical substance. By accomplishing this proposed research as the first step of the long-term goal, it will demonstrate that the fMALDA developed is a useful approach to work together with the general enviromental sampling settings for UFP-related environmental health studies. The proposed research is innovative because the fMALDA developed will enable systematic UFP respiratory deposition experiments to be done in urban communities to facilitate more accurate inhalation dosimetry estimation on UFP-related chemical substances.